1. Field of the Invention
The present invention relates generally to a flow prevention apparatus for damaged fire hydrants, and more particularly, to an adjustable flow prevention apparatus for a wet barrel fire hydrant where damage to the water system elements is avoided while shut off of water flow from a damaged hydrant is simultaneously achieved.
2. Description of the Related Art
There are two basic types of fire hydrants manufactured today. These two types are commonly referred to in the trade as the “wet” barrel or “California” fire hydrant and the dry barrel fire hydrant. As the name implies, wet barrel fire hydrants are always supplied with water under pressure from a municipal, or other supply, water system. As such, it is the practice to install this type of fire hydrant only in milder climates where there is no chance of freezing. Because wet hydrants are constantly supplied with water, however, damage to the hydrant can result in a considerable loss of water before the damaged hydrant is discovered and repaired.
Where the climate is dry, or where drought conditions prevail for any length of time, manufacturers of wet hydrants have endeavored to provide flow cut off devices to prevent loss of water in the event of damage to the barrel, such as may result from a vehicle collision. Unfortunately, the probability of such events occurring is quite high due to the standard location of hydrants adjacent the street curbs to facilitate rapid access by fire department personnel in the event of a fire emergency. Therefore, in the construction of wet barrel hydrants, manufacturers have proposed the use of cut off valves that are actuated in response to a pressure drop which will occur when, for example, the barrel is broken off from the supply pipe. In other arrangements, a valve is actuated by a mechanical linkage between the barrel and the cut off valve so that when the barrel is removed, such as by a vehicular collision or similar event, the valve will be quickly shut to prevent any significant water loss.
With these and other devices, however, damage to the pipes and valves in the system can occur as a result of the high pressure that these elements experience due to the sudden closing of a supply pipe when the cut off valve is actuated as a result of the abrupt change in flow velocity of the water. Such an abrupt change produces what is commonly referred to as water hammer. Water hammer refers to the pressure fluctuations associated with the change between the kinetic energy of moving water and pressure energy, which may be either positive or negative. When the water in the pipe is stopped abruptly, considerable force is exerted on the valve and oscillating shock waves are reflected back into the municipal water system. The tremendous forces associated with water hammer can destroy the valve and damage other seals and pipes throughout the water system.
Accordingly, systems have been developed to reduce the effects of water hammer. In some systems, it has been proposed to provide an upstream cut off valve that can be actuated gradually or even manually to prevent such water hammer damage. These arrangements, however, can result in substantial down stream water loss through the broken hydrant which is clearly undesirable in areas suffering drought and may also require cut off of flow to undamaged hydrants as well.
In other arrangements, water cut off devices have been proposed which are warranted to cut off flow to a damaged hydrant but such devices are often difficult and expensive to install particularly in older, established water systems. For example, U.S. Pat. Nos. 4,127,142 and 4,596,263 both disclose wet barrel systems that utilize a dash-pot assembly connected to a “swing check” or flapper type valve. The valve is biased toward the closed position by a spring and is held open and out of the flow passageway by a holding bar connected to the upper barrel of the hydrant. If the hydrant is sheared from its support, the holding bar releases the flapper valve and the spring urges the valve into the flow passageway. The valve then closes due to the resulting change in water pressure, while the dash-pot assembly prevents rapid closure of the valve.
Although the systems disclosed by U.S. Pat. Nos. 4,127,142 and 4,596,263 reduce the effects of water hammer, they still have limitations. For example, if the hydrant is merely damaged, rather than completely sheared off, the holding bar may actually prevent the valve from closing. In addition, the above systems require an underground barrel with a lateral chamber to accommodate the arrangement of the dash-pot assembly. Such an arrangement makes the use of the disclosed systems more difficult and expensive to install with existing water systems and/or with systems of different sizes or types. Finally, once the dash-pot assembly is installed, the restrictive rate of closure of the flapper valve cannot be adjusted.
What is needed then, is an adjustable cut off valve for a wet barrel hydrant which is simple to install and relatively inexpensive, and that will effectively cut off water flow without causing water hammer in the accompanying system. It is to such a device that the present invention is primarily directed.